When devices such as an inverter, a circuit breaker, and an electromagnetic switch are combined and used in a control panel or a switchboard etc., power and signals such as control signals are transmitted through cables connecting between the devices. Each of the devices has a terminal for connecting a cable. Signal transmission between the devices is carried out by connecting the cable to the terminals. In this case, in general, for maintenance and from an appearance point of view, a cable duct that houses the cables is provided, and through the cable duct, the cables are transversally laid and passed between the devices. In the following Patent Documents 1 and 2, configurations are disclosed in which devices are connected by cables through cable ducts and a duct cover is mounted on a duct body.